1. Field of the Invention
This invention relates to solid state tunable lasers, and, in particular, to chromium (III) ordered perovskite lasers and media therefor. Accordingly, it is a general object of this invention to provide new and improved lasers and media of such character.
2. Description of the Prior Art
The class of tunable solid state lasers, which are based on vibronic transitions (i.e., involving both electronic and vibrational changes of state) in metal ions, are of interest. With the exception of chromium in alexandrite, it is believed that the majority of such lasers were discovered some 15 years ago.
"Phonon Terminated Optical Masers", by L. F. Johnson, H. J. Guggenheim, and R. A. Thomas, Phys. Rev. 149, 179 (1966) sets forth a summary of characteristics of phonon-terminated optical masers in Table I thereof, including active ion Ni.sup.2+ with hosts MgF.sub.2, MnF.sub.2, and MgO, active ion Co.sup.2+ with hosts MgF.sub.2, ZnF.sub.2, and KMgF.sub.3, and active ion V.sup.2+ with host MgF.sub.2. These sources, which provide radiation in the red and near-infrared portion of the spectrum have been "rediscovered" in the past few years. Still, the lasing ions (Ni.sup.2+, Co.sup.2+, V.sup.2+) and the hosts (MgF.sub.2, MgO, KMgF.sub.3) have remained exactly the same as in 1966. All of them operate only at cryogenic temperatures.
A laser based on chromium in alexandrite (BeAl.sub.2 O.sub.4) has been described in a paper entitled "Tunable Alexandrite Lasers" by John C. Walling et al., IEEE Journal of Quantum Electronics, Vol. QE-16, No. 12, December 1980, pp. 1302-1315. Also of interest is U.S. Pat. No. 3,997,853, issued Dec. 14, 1976 for "Chromium-Doped Beryllium Aluminate Lasers".
The amount of chromium which can be accepted as a dopant by alexandrite is about 0.3 wt%. When more chromium is used with alexandrite, the efficiency of the device degrades.
There are several significant characteristics of alexandrite: (1) It is a hybrid material with the Cr.sup.3+ 2 E and .sup.4 T.sub.2 electronic states at almost the same energy, the .sup.4 T.sub.2 being only thermally populated and being above .sup.2 E, thereby leading to low emission cross-sections from the .sup.4 T.sub.2. (2) There are two crystallographic sites for chromium, only one of which is active in the laser (thereby reducing by fifty percent the effective concentration of the active ion). (3) It undergoes severe concentration of quenching above about 0.3 wt% doping.
A known class of fluidic tunable lasers include so-called dye lasers. Dye lasers, tunable in the visible spectrum, are useful and effective, but have limited commercial applications. They are not susceptible to Q-switched operation. Since dyes are in a liquid medium (usually alcohol, a typical solvent), they undergo photodegradation, and have to be periodically replaced.
The few different types of solid state lasers, known in the art, are believed to produce essentially single frequency light. Neodymium (infrared) and ruby (visible) are single frequency devices; they are not tunable. A known class of solid state lasers includes so-called F center lasers. These lasers, as a class, are collectively tunable in the region 0.7 .mu.m to 3.5 .mu.m. Although these devices are solid state, the active media frequently must be stored at cryogenic temperatures and they can be operated only at cryogenic temperature. Also, like organic dyes lasers, they cannot effectively be operated in a Q-switched mode.